Permeability fines migration

Other minerals beside water-swelling clays have been found to undergo fines migration. The permeability damage caused by essentially non-swelling clays such as kaolinite and chlorite is a well-known phenomenon. Silica fines have been identified as a potential source of permeability damage in various poorly consolidated U.S. Gulf Coast formations (1). Other minerals identified as constituents of mobile fine particles include feldspar, calcite, dolomite, and siderite (4,5). 

Core floods were performed to determine if treatment polymers would prevent permeability damage caused by fines migration within consolidated rock and whether the adsorbed polymers would themselves reduce core permeability. The tests were performed using Hassler sleeve chambers. With the exception of the polymer... 

Fines production from untreated test sands and permeability damage observed in untreated cores indicated that the laboratory test flow rates were above the critical flow velocity required to initiate fines migration. 

Results indicated that swelling clay stabilizers such as poly (DMA-co-EPl) which do not possess a quaternary nitrogen atom in a pendant chain may not be very effective at preventing permeability damage due to fines migration in the absence of water-swelling clays. 

Permeability Reduction in Presence of Oil. Muecke (55) and Sarkar and Sharma (56) examined permeability reduction due to chemical fines migration in Berea core samples saturated with brine and at residual oil saturation. Liu and Civ an (49) modeled permeability impairment due to salinity shock with and without the presence of residual oil. In the first experiment, fresh water was injected into a Berea sandstone core saturated with 3 wt% sodium chloride. In the second experiment, the fresh water was injected into a similar core at residual oil saturation. Figure 4 shows that their model predicted the experimental data fairly... 

Figure 3. Permeability decline due to chemical fines migration. (Reproduced with permission from reference 29. Copyright 1983.)...

Production of petroleum is often hampered by damage to the permeability of reservoir rocks resulting from interaction of injected fluids with the porous rock formation. Fine particles of clays and other minerals are often found attached to the pore walls of reservoir rocks. The interaction between injected fluids and the rock can cause their movement by a combination of mechanical shear forces, colloid-chemical reactions and geochemical transformations. This chapter reviews several different aspects of the fines migration process. 

Experimental Studies of Permeability Damage by Mechanical Fines Migration... 

Effect of Rock Characteristics. Rock characteristics that affect mechanically induced fines migration include the following absolute permeability, pore geometry and pore size distribution, size distribution of fines, amount and type of fines present in the rock, and the location of fines with respect to the pores. 

In unconsolidated sand formations, the net overburden pressure also appears to affect fines migration. Coskuner and Maini (42) reported that the critical velocity at which permeability damage is initiated decreases... 

Fines Migration in Multiphase Flow. Most of the preceding discussion was concerned with flow of brine at 100% brine saturation. From a petroleum engineering perspective this brine staturation represents a condition that is rarely encountered in the field. A more relevant situation would be flow of brine at residual oil saturation and commingled flow of oil and brine. When fines migration occurs in the presence of two immiscible fluids, additional factors such as the wettability of the medium and that of the fines and the relative permeability characteristics become important. Therefore, it is important to consider the effect of the presence of a second immiscible fluid on fines migration and permeability damage. 

In agreement with the statements made regarding the influence of hydrodynamic forces in the previous section, Khilar et al. (18, 36) have found at best a weak dependence of CSC on the superficial velocity (for 3 to 568 cm/h). Because in practise one deals with solutions of mixed salts, Khilar et al. (18) have introduced the critical total ionic strength (CTIS) to improve the predictions for solutions containing multivalent ions such as calcium. A number of studies have shown that where freshwater flooding of sandstones may drastically decrease permeability due to fines migration, suitable adjustment of the flooding solution composition to above the CSC or CTIS can decrease or eliminate the permeability reduction (12, 18, 36). In these cases the solution compositions are adjusted so as to reduce the Zeta potential at the particle surfaces, which reduces the repulsive colloidal forces. Thus the same factors that... 

Effect of pH. The pH of the flowing fluid is an important factor in the fines migration process (5, 12, 52, 58). Mungan (52) noted that injection of strong acids or bases could cause permeability damage. Under very high or very low pH conditions, the permeability damage is caused by dissolution of the matrix material, which produces fine particles of varied mineral composition. Somerton et al. (58) found that the water sensitivity of reservoir sands was related to the pH response exhibited by the rock after the contact with fresh water. Most sandstone cores showed an increase in the effluent pH after the switch was made... 

---